Add type assert to SparseContainers for inference

Author: charleskawczynski

src/sparse_containers.jl

@@ -3,7 +3,7 @@
     SparseContainer(compressed_data, sparse_index_map)
 
 A compact container that allows dense-like
-indexing into a sparse container.
+indexing into a sparse, uniform, container.
 
 # Example
 
@@ -17,18 +17,22 @@ v = SparseContainer((a1,a2,a3,a4), (1,3,5,7))
 @test v[1] == ones(3) .* 1
 @test v[3] == ones(3) .* 2
 @test v[5] == ones(3) .* 3
-@test v[7] == ones(3) .* 4```
+@test v[7] == ones(3) .* 4
+```
 """
-struct SparseContainer{T,SIM}
+struct SparseContainer{ET, SIM, T}
     data::T
     function SparseContainer(compressed_data::T, sparse_index_map::Tuple) where {T}
-        return new{T, sparse_index_map}(compressed_data)
+        @assert all(map(x-> eltype(compressed_data) .== typeof(x), compressed_data))
+        return new{eltype(compressed_data), sparse_index_map, T}(compressed_data)
     end
 end
 
 Base.parent(sc::SparseContainer) = sc.data
-@inline Base.getindex(sc::SparseContainer, i::Int) = _getindex_sparse(sc, Val(i))
-@generated function _getindex_sparse(sc::SparseContainer{T,SIM}, ::Val{i}) where {T, SIM, i}
+@inline function Base.getindex(sc::SparseContainer{ET}, i::Int) where {ET}
+    return _getindex_sparse(sc, Val(i))::ET
+end
+@generated function _getindex_sparse(sc::SparseContainer{ET,SIM}, ::Val{i})::ET where {ET, SIM, i}
     j = findfirst(k -> k == i, SIM)
     j == nothing && error("No index $i found in sparse index map $(SIM)")
     return :(sc.data[$j])